The present invention relates to a method for transferring an object levitated by sound waves.
Japanese Unexamined Patent Publication Nos. 7-24415 and 7-137824 describe apparatuses that levitate objects. Each apparatus employs a plate-like vibrator to generate sound waves and levitate an object with the sound waves. The sound waves are directed toward the object, which has a flat surface opposed to the vibrator. Further, apparatuses used to transport levitated objects have also been proposed. One apparatus blasts air against a levitated object to transport the object, and another apparatus uses a carriage, which is provided with a device that levitates an object, to transport the object.
When a levitated object is transported to a predetermined location by a transporting apparatus and then transferred from the apparatus to another location, it is preferred that the object be transferred in the levitated state. This reduces the possibility of the object being scratched or smeared. To receive an object from the transporting apparatus in a levitated state, an unloading apparatus provided with a device that levitates the object may be employed. However, when the unloading apparatus receives the levitated object from the transporting apparatus, the transfer of the object between the transporting apparatus and the unloading apparatus may become unstable when the unloading apparatus approaches the object from below.
The levitating force of the sound waves generated by the vibrator is strong in an area proximal to the vibrator where the distance from the vibrator is 50 to 500 micrometers. This area is defined as a near-field. The sound waves generated by the vibrator include a (quasi) standing wave, which has wavelength xcex. In addition to the near-field, the levitating force is strong at positions corresponding to n times (n being a natural number) one half the wavelength xcex of the standing wave. These positions are defined as peak positions. The levitating force in the near-field is stronger than that at the peak positions. Accordingly, when the vibrator of the unloading apparatus approaches the bottom surface of the object, the vibrator levitates the object when the object reaches any one of the peak positions. The levitating force at each peak position is weaker than that at the near-field. Thus, if an unexpected force is applied to the levitated object for one reason or another, the object may move into the near-field from its proper position.
When the levitated object is flat and has a large surface area, it is preferred that a plurality of vibrators be used to levitate the object. However, it becomes more difficult to stably unload the object as the number of vibrators increases.
It is an object of the present invention to provide a method and apparatus that stably transfers an object levitated by sound waves from one place to another.
To achieve the above object, the present invention provides a method for transferring an object levitated above a transporting vibrator from the transporting vibrator to a platform. The transporting vibrator generates sound waves to produce a transporting levitating force that levitates the object. The method includes arranging the platform at a predetermined position below the object. The platform is provided with an unloading vibrator, the object has a bottom surface, and the unloading vibrator has a top surface. The predetermined position is determined so that the distance between the top surface of the unloading vibrator and the bottom surface of the object is less than one half the wavelength of a standing wave generated by the unloading vibrator. The method further includes moving the platform upward toward the object from the predetermined position, and levitating the object above the platform when moving the platform upward. The unloading vibrator generates sound waves to produce an unloading levitating force that levitates the object. The method also includes moving the object levitated by the platform to a position at which the transporting levitating force does not affect the object.
A further perspective of the present invention is a transfer apparatus for levitating an object with a force produced by sound waves. The transfer apparatus includes a transporting device for transporting the object. The transporting device includes a transporting vibrator for generating a transporting levitating force. The transporting vibrator has a top surface, and an unloading device for unloading the object from the transporting device. The unloading device includes unloading vibrators and a plurality of spaced, parallel prongs for holding the unloading vibrators. The unloading vibrators generate an unloading levitating force. The object has a bottom surface, and the unloading vibrators each have a top surface. The prongs are arranged at a predetermined position to unload the object from the transporting device. The predetermined position is determined so that the distance between the top surface of each unloading vibrator and the bottom surface of the object is less than one half the wavelength of a standing wave generated by the associated unloading vibrator. The prongs elevate to levitate the object with the unloading levitating force and move the object to a location where the transporting levitating force does not affect the object. The unloading levitating force is produced in an area proximal to each unloading vibrator.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.